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Hello, everyone. I'm Mr. Tony, who only talks about technology and doesn't cut his hair. Recently, a friend shared that he participated in the internship interview of data analyst of an Internet (live delivery) company. The following is my analysis of relevant SQL test questions. The database used is MySQL 8.0. If you find the article useful, ...

SQL basic knowledge sorting select query results, such as:   [student number, average score: group function AVG (score)] from which table to find data, such as: [related to grade: grade table score] where query criteria, such as: [b. course number = '0003' and b. score > 80] Group by grouping, such as: [average of each student: gro ...

1. Stored procedures and stored functions      1. Stored procedure and stored function: MySQL provides the mechanism of stored procedure and stored function. Let's collectively call stored procedure and stored function stored programs. Unlike ordinary SQL statements, which need to be compiled first and then executed immediately, ...

During data query, the console reports caused by: com.mysql.cj.exceptions.wrongargumentexception: hour_ OF_ Day: 0 - > 1 exception. The query shows that this is caused by querying the MySQL database and converting the field type to datetime.There are many online solutions, most of which are solved by setting the time zone. Unfortunately, thr ...

Students of background development and operation and maintenance are certainly familiar with MySQL backup. Regular online database backup is necessary, and this process is generally automatic. This paper will introduce a shell script, which has the function of automatically backing up MySQL and automatically clearing expired backup data Back ...

preface When building a mysql Cluster, a single master makes master-slave replication, which greatly improves the reading and writing ability of the database, but once a single point of failure occurs, the whole cluster will be paralyzed. Therefore, we usually configure the master to improve the redundancy ability of the cluster. 1, W ...

1, Master slave replication          There is a close relationship between master-slave replication of MySQL and read-write separation of MySQL. First, deploy master-slave replication, only master-slave replication Only after the replication is completed can the data be read and written separately on th ...

Welcome to personal blog http://www.jkraise.top This case project is based on MySQL and Redis in the dark horse headlines Database optimization 1. Slicing2. Vertical split3. Horizontal split Slice effect Sharding is also called data sharing. Its main work is to split a single database and a single table. Multiple databases and tables toge ...

catalogue 1, Sort by keyword 1. Single field sorting 2. Multi field sorting 2, Or / and Application 3, Query non duplicate records 4, Group results 5, Limit result entries 6, Set alias Usage scenario 7, Join statement 8, Wildcard 9, Subquery 1. Definition 2. Subquery - alias 3. Subquery - exists 10, View 11, NULL value 1. Defi ...

MySQL built-in constraints and functions 1. Table constraints In order to ensure that the database is inserted according to the specified rules, table constraints are introduced in the database. Common table constraints are The primary key constraint primar key (cannot be empty or duplicate) if it is an integer type, it is generally defined ...